This proposal uses knowledge gained from extensive research into the activity of the influenza virus NS1 protein, to devise a strategy that will lead to the discovery of new influenza virus drug candidates. It is widely acknowledged that the consequences of an influenza pandemic could be devastating and that we do not have sufficient therapeutic resources available. Widespread resistance to the M2 inhibitors, and most recently to the neuraminidase inhibitors as well, makes it imperative that we develop new and improved antiviral drugs against influenza virus. We propose to use the influenza virus NS1 protein as a novel target for the discovery of the next generation of antiviral drugs. NS1 functions as an inhibitor of the innate immune response and its actions ultimately determine disease severity in the infected host. Specifically, NS1 prevents the production of interferon in response to virus infection. Influenza viruses that lack NS1 do not cause disease as the host immune response (the most powerful natural antiviral) can function normally and eliminate the virus. Thus, we reason that compounds which inhibit the interferon inhibitor, NS1, should work similarly to prevent virus growth and disease progression. We have developed a cell-based reporter assay for monitoring NS1 function which we will use to screen libraries of small molecular weight compounds and identify those that reduce the immune-suppressing actions of NS1. Such compounds represent new influenza virus drug candidates that can be further evaluated and developed to determine their full potential. PUBLIC HEALTH RELEVANCE: Influenza viruses cause a highly contagious, acute respiratory disease that affects 5-20% of the US population each year. There is heightened concern regarding resistance to both of the two classes of FDA-approved influenza antiviral drugs and therefore we are in great need of new antiviral drugs to treat and prevent influenza infections. In this proposal we describe using the influenza NS1 protein as a new target for finding the next generation of influenza antiviral drugs.